When power is first applied to electric motor systems they experience a large spike in (or a “rushing in” of) electric current of, e.g., 150 Amperes or more caused by the initial charging of their bus capacitors. Unabated, this inrush of current can damage the system's electrical components. Some systems use an inrush resistor electrically connected in series with the power source to ameliorate the effects of the inrush of current. Once the bus capacitor is charged and the inrush of current ends, the inrush resistor is removed from the circuit by an inrush relay that closes to create a short circuit around the inrush resistor. However, if the inrush relay fails to close, such that the inrush resistor remains in the circuit, then the inrush resistor can experience increasing levels of power and heat as the load increases and the motor draws more current through the inrush resistor. At higher power levels the inrush resistor may burn out, but even at lower power levels the inrush resistor may generate substantial heat.
This background discussion is intended to provide information related to the present invention which is not necessarily prior art.